Thermionic amplifier



H. DE F.VARNOLD..

THERMIONICAMPLIFI EB. ARPLlCATlON FILED JULY 30, 19:8-

Patented Jan. 27; 1920.

UNITED STATES PATENT OFFICE.

HAROLD im r. A NOLD, or MAPLEWOOD, NEW JERsEmnssroNOB. To WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y A CORPORATION 0}? NEW YORK.

Tmmirromc AMPLIFIER.

Specification of Letters Patent. Patented J an. 27, 1920.

Continuation in part of application Serial No. 841,567, filed May 28, 1914, and application Serial No. 841,568,

,qua May as, 1914, patented March 2,

To all whom it may concern:

Be it known that I, HAROLD DE FOREST ARNOLD, a citizen of the United States, residing at Maplewood, in the county of -ES- sex and State of New Jersey, have invented certain new and useful Improvements in T'hermionic Amplifiers, of which the following is a full, clear, concise, and exact description.

This invention relates to thermionic amplifiers of the audion type, and its object is to provide a structure by which certain desired characteristics of the amplifier may be secured at will and in an eflicient manner. This object is accomplished by proportioning the geometrical and electrical relations of the various elements of the device in a manner more fully explained later in this specification.

In order that the novelty of this invention may be appreciated, and that those skilled in the art may be enabled to use this invention tobest advantage, it is necessary that certain terms hereinafter used shall be defined. The following brief discussion is intended to explain the operation of the device and to'define the terms to be employed.

The thermionic amplifier consists of. a hot electron-emitting cathode, such as the so-called Wehnelt cathode, of a cool anode and of an auxiliary electrode called the grid, which is usually, though not always,

located between the anode and the cathode.

A battery is connected so as to force the electrons liberated at' the cathode toward the anode, thus setting up a convection current carried by electrons in the evacuated I space. In this specification since only the structure of the device itself is under discussion, only the efiects of changes 1n that structure are cons1dered. Obviously a change in the battery will also change the characteristics of the circuit, but in a way which is already known in the art. Due to the presence of these electrons, a negative space charge is established between the anode.v and the cathode, whose efiect is to limit the v number of electrons which can leave the cathode, and consequently to limitalso the- .current which can flow in" the output cir-" cuit, by which is meant the circuit including the battery and the path of the space current. The object of the 'gridis to fur nish a means for introducing a further 1915. This application filed July 80,

lized: in fact, a transformer is 1918. Serial No. 247,422.

negative charge into the anode and the cathode, or for introducing into it a pos1t1ve charge which shall neutralize the effect of part of the space charge due to the electrons. convection current is 0nd it is increased.

charge to the grid, a source of electromotive force is connected between'grid and cathode, that is, between the input terminals of the device. The effect of such an impressed electromotive force is therefore to alter the magnitude of the space current 1n the amplifier by changing the distribution of space charge between the electrodes, and moreover this is accomplished Without requirlng that the impressed electromotive force shall do more work than that involved in forcing the charge to the grid against the counter voltage of the condenser formed by grid and filament. Since in this operation the change in power consumed in the output circuit may be much greater than that required in charging the condenser, the device acts as an amplifier. This variation in space current, due toan impressed electromotive force, willhereafter be called the output current of the amplifier and the variation in Voltage, which appears in the Output circuit due to the impressed electromotive force, -.will be called the output voltage. The reason for adopting these definitions is that in the practical applica- In the first case, the decreased; in the sections of the amplifier it is only these variations in current or voltage which are utiordinarily used to derive power from the output circuit, and obviously the steady space current or the steady output Voltage have no effect inthe secondary ofthat transformer and may be ignored for practical purposes. Thus, the term voltage amplification means here the ratio of the alternating voltage appearing in thesecondary of suclt a unity ratio transformer to the alternating voltage impressed across the filament and grid, when the transformer primary is made to include the whole of the output; circuit external to the amplifier. In simpler terms, it is the ratio of the above defined output voltage to the impressed input'voltage- There will also be occasion to consider the ratio .of output current to input voltage, the

latter being taken as standard throughout.

space between the} In order to force this voltage amplifying When this ratio is high, other things bein the same, the amplifier will be said to be -'0 the high current type, and vice versa. This latter ratio is, of course, not a pure number, but is of the nature of an admlttance. I It has been found that amplifiers may be designed for given circuit conditions so that they will have whichever of the above mentioned characteristics is desired. That is, one may be designed to deliver to a receiving device a comparatively high volta with a low current, or vice versa. T e principles of operationwhich have been'discovered which enable thisresult to be aclbicomplished ma be stated as follows.

ace it has been found that it" In the first p locate the grid as near is of advantage to the cathode as possl voltage amplification or outputcurrent. In practlce it been'found that when the two elements are'se arated only by a mere oxidlzin'icoating t e most efficient action is obtaine Unless there is a solid and continu-- "ous spacing element between the two itmay be necessary of course to separate them a small distance to prevent actual contact bej tween them due to forces'set up during operatio'n. By sayingthat the elements are, placed, as close together as possible it 1s meant that the distance between them is made as small as possible without introducappreciable electrical or mechanical dis,

turbances during operation.

Again, it has found that,' when the cathode and grid are placedas near to each .otherfas possible, decreas' from the anod'e'to the catho e decreases the power of the tube .without at the samelmereducing the variable is, ifwe'.consider .two tu has the. anode current set up in the outppt circuit. ,That s, one. of which and cathode'widely spaced 7 while the other has them near together, the

covered.

:grid being .very close to the cathode in each case, tliefirst'tub when installedin a system of the usual kind tends -to cause marked voltage amplification, while the latter if substituted for, the former increases the variable current output and at the same time lowers the voltage amplification.

A third principle of operatlon of the ther- 'mionic repeater which crease the variable output current increase principle mum efliciency is obtained'when the impedance between the anode and cathode is.

equal to the total impedanceof the variable 'ble whatever the desired the distance current consumption circuit. This total impedance includes the total line impedance and that of the receiving or translating device or devices to which power is ,being supplied.

It hasbeen found that tubes maybe constructed in such manner as to take advantage of any number or of all of the above.

mentioned' principles with, of course, corregpfindingly increased efliciency and adapta- Anobjectof this invention is to provide .1

an audion, or. an equivalent device, which the variable energy supplied thereto without at the same time causing a will amplify large voltage am lification, as in systems of this type hereto ore used. or, differently stated:

To-'provide an audion, or e uivalent der vice, which'will cause the amp ified ener which appears in the output circuit t'o-ta e the form of large variable current, rather than smaller variable current with large voltage amplification. Y

' Another object is t provide an audion, or equivalent, system by which a proper impedance ratio is obtained between the impedance of that portion of the output circuit which is without the audion and that of the remaining portion of the external circuit, whereby a greatly increased efliciency is obtained.

A further object of the invention is to provide an audion, or equivalent device, which will operate with increased efliciency when thetranslating deviceto which the amplified ener%y' is supplied in the output circuit of the evice is one which operates best upon maximum variable current, as distinguished from one which operates best upon maximum variable voltage.

Another object of the invention is to provide an audion, or equivalent device,.which .will operateefiiciently with a current operated translating device without the use of a voltage transformer between the audion and thetranslating device. 1

Viewed broadly, the invention provides.

for an increaseof the efliciency of an audion,

by reference to the following specification taken in connection with the accompanying drawing in which Figure l represents the structure of an amplifying tube which is designed to give greater voltage amplification than those of the prior art; Fig. 2 is a plan view of the amplifier of Fig. 1 arranged to exhibit the geometrical configuration; Fig. 3 1s a view of a tube structure designed to give a large output current with low or negative voltage amplification; Fig. 4 is a plan-view of the structure of Fig. 3;. Figs. 5 and 6 are views corresponding to Figs. 3 and 4 respectively of a modified structure of the new type of amplifier; Fig. 7 is a circuit diagram showing an amplifying system making use of an amplifier of the type shown in Fig. 1; Figs. ing several forms of circuit making use of an amplifier of the kind shown in Fig. 3.

In these figures, like numerals represent corand 3 the anode or plate.

responding parts.

Referring to Figs. 1 and 2, 1 represents the grid element, 2 the cathode or filament The plate is placed a considerable distance from the cathode, and the grid is placed very close to the cathode and may be separated therefrom only by a thin insulating film as, for example, an oxidizing coating on one or the other of these elements. Further, the grid is made to have afine mesh and thus to obstruct greatly the view of the plate as seen from the cathode.

Figs. 3 and 4 are two views of a thermionic amplifier of the high current type. In these structures, in conformity with the above mentioned principles, the distance from plate 3 to cathode 2 is made very small, and the grid is placed as close as possible to the cathode. Further, the grid 1 is made to have a coarse mesh, or is constructed to have a large ratio of open space to conducting surface, as is required by the conditions above set forth for this type of amplifier.

Figs. 5 and. 6 show another modification of the high current type of amplifier. The input electrode or grid is in the form of a wire 1", bent back at its middle. In effect, therefore, the input electrode consists of two Wires joined together.- The filament 2 is wound about the input electrode and is insulated therefrom by a tube of insulating material 4:, an arrangement which is not the invention of this applicant, but is described and claimed in Patent 1,169,422 of Jan. 25, 1916 to Alexander McLean Nicolson. The output electrode or anode consists of two plates 3 3" arranged upon opposite sides of the filament and close to it. It will be noted that the in'put'electrode is not located between the filament and plate, such not being necessary in this high current type of tube.

Fig. 7 is a diagram of an amplifying system in which a tube Vof the type shown in Fig. 1 is employed. The tube has the usual input circuit 4, 4 and output circuit 5, 5. The exact arrangment of input and, output 8, 9 and 10 are circuit diagrams showvariable current and circuits is that shown in Page 1,129,942

systems of the types shown in Figs. 7 and 8 "respectively of this application, such combination having marked advantages for certain purposes specified in said patent. The purpose of the present application is to specifically describe and claim these types 5f systems employing novel thermionic-amplifiers, use than that disclosed and claimed in the above mentioned patent;

A source-of potential 7 may be inserted in the input circuit to bring the'grid to a desired initial or working potential. N 0 transformer need be used, the incoming-line being directlyconnected to the input elec-' trodes, and the outgoing line, to the output electrodes. A high resistance element 6 may be connected across the input circuit as shown. A coil 8 of large inductance provides a path for direct current for the tube V, such current being supplied by a source- B. The coil 8'will not conduct an appreciable amount of the variable current in the output circuit owing to its high impedance to such current. The condenser 9. is inserted in the line to prevent flow of direct current from the source B through the receiving device 10 if the latterdoes' not itself prevent such fiow.

The receiving device 10 may be one which operates most efficiently upon high variable voltage and low current. In accordance with the principles discussed above, the grid 1 and cathode 2 are placed very close together while the plate 3 is widely sepathese being capable of more general rated from the cathode, the distance between necessary to give the deimpedance and accordingly the impedance of the tube between filament and plate is made high, the two impedances being.

voltage output charac-- made as nearly the same as possible consistent with other possible conflicting requirements. They should at least be of the same order of magnitude, for example one being 100,000 ohms and the other 25,000 ohms. The rct'eiving device 10 may be a second amplifying tube or similar device.

Fig. 8 is a diagram of a system the same as that of Fig.7 except that areceiving device having relatively low impedance or operating eificientl'y low voltage, or both, is present. Accordingly, the anode 3 and cathode 2 of the tube are placed relatively upon relatively large very close to the cathode. he impeda of the amplifier between filament and plate is made t e same as that of the receiving device 11, or as nearly the same as other operating conditions will permit, and at least of the same order of magnitude.

It has been found that in accordance with this invention an amplifier of the type will develop amplified energy at a voltage 1 one third of thelvoltage of the input en-.

shown in Fig. 8 may. be constructed which ergy and having an. anode-to-cathode impedance as low as 500 ohms. Such an amplifier can, ,then, be worked eflic'iently into a receiving device or line having this rela- '-tively low impedance and the eflicien'cy with ,a receiving device of even much lower 1m-.

- pedance would relatively high- -much systems .3 5

higher than that heretofore attainable.

Fig. 9 shows the same circuit as Fig. 7 except that a high resistance element 13 is substituted for the coil 8, this resistance being so large that the variable current through it is negligible.

is here shown, a tube impedance of the same order as thatof the telephone receiver 15 being thus obtained. g

In Fig. 10 is-shown a system similar to that of Fig. 8 except that input and output.

transformers 16 and 19 respectively, are employed.

some time.

closed, the tube being Fig.8. The impedance of the primary winding 17 of the transformer 19 is low. and

accordingly the cathode-to-anode impedance is made of the same order, the ratio of '17 being the same as the number of turns of coil 18 to that of coil the ratio of the .impedance of receiving device 15 to that of the primary winding 7 dynamo B is here shown as .the 'source of space current, it being understood of course,

that the type of source used is immaterial. An impedance coil 22 may be inserted m series with the source B to reduce the ouramount. 1 'By thermiomcrepeater is meant a repeater dependin'g for its operation upon rent vanations set up by therommutator of the mach These variations may be of frequency riuite different than that of the variable cur out set up. by'the tube V, .so that the .coil 22 may discriminatebetween them. If rthe impedance of the primary 'coil 17 is high, as might be the case if it were desired-to use a step down transformer,

the cathode-to-anode impedance of the tube V would of course be increased the desired near together, the grid 1' as before" The high-current," low-voltage-amplification'type of ampllfier- 18. -A directcurrent.

current discharge from a heated cathode.

It is obvious, however,'that the invention .might be applied to. a discharge device in which other means is employed for liberating electrons from the cathode. 'In its" broadest aspect the invention is not limited to the particular structure herein illustrated, but may be found useful in modified:

forms or typesof discharge tubes and in connection with a variety of circuit arrangements;

What is claimed is:'

1. A thermionicdi'scharge tube having a cathode, an anode and a controllin e cotrode, said anode being located in suc close proximity to the cathode that the tube operates -to produce energy amplification without substantial voltage amplification.

2. A thermionic discharge tube havin a cathode, an anode, and a controlling'e ec trodey said controlling electrode and said located in such close proximityanode being to the-cat ode that the tube operates to produce energy amplification withoutsub- 'stantial voltage amplification.

3. A thermionic discharge tube having a cathode, an anode and a controllin electrode, said anode being located in suc close proximity to the cathode as to keep the in-.

ternal impedance of the tube sufficiently low to permit of energy amplification without substantial voltage amplification.

.4. The combination with a thermionic discharge tube having a cathode, an anode, and an impedance varying element, of an input circuit and an output circuit therefor,

1 means for producing. a variable electromotive force in said input circuit, a source of electromotive force in said output cirthe variable current of said output circuit, sa1dcathojde being located so close. to both said anode and said impedance varying element, that, for the impedances and voltagescuit', and translating means for utilizing employed outside the tube, the tube oper- I ates to amplify the energy in said input circuit without amplifying the voltage. v

5. The combination with a thermionic discharge device having'an anode, a cathode anda grid, of an input circuit andan output circuit therefor, means for producing a circuit, 2.,80111'06 of electromotive force in said output circuit, and translating means for utilizing the variable current of said output circuit, said cathode being placed so close to said grid and said grid-being ofvariable electromotive force in said input such fine mesh that,;for the impedances and voltages employed outside saiddevice, the device operates to amplify the variable .energy in said input circuitwithout amplifying the voltagel 6. The combinationy-with a thermionic.,-

discharge tube having a cathode, an anode naaaass and an impedance varying element, of an inputcircuit and an output circuitztherefor,

means for producing a variable electromotive force 1n said mput circuit, a source cf electromotive force in said output 'clrcuit,

and translating means for utilizing the variable current 0 said output circuit, said impedance varying element being in immediate proximity to the cathode but outof electrical contacttherewith, and closer to t V cathode than'to the anode, so that for the and said catho e is of the same order as that of said outgoin circuit.

discharge device, having an'anode, a cathode and a control element, of an input circuit therefor, and an outgoing circuit having impedance'and connected to said anode and cathode, said cathode, anode and control ele-, ment being so spaced that the impedance of said discharge device between said anode and saidcathode is approximately the same as that of said outgoing circuit. a

9. The combination with a thermionic discharge device having a cathode, ananode,

and acontrol element, of an input circuit connected to said cathode and said control element, an outgoing circuit having impedance and connected to said anode and cathode, a source of electromotive force in said outgoing circuit,' and means for impressinga varying electromotive iorce upon said input circuit, said cathode bemg placed 1n immediate proximity to said control ele-- ment but out of electrical contact therewith, and said anode being so spaced from. said cathode and control element that the impedance of said discharge device between said anode and said cathode is of'thesame order as that of said outgoing circuit.

10. The combination with a thermionic said cathode and said grid, an outgoing circuit having impedance and connected to said anode andcathode, a source of electromotive force in said outgoing circuit, and means for impressing a varying electromotive force upon said input circuit, said cathode bemg laced in immediateproximity to said grid but out of electrical contact therewith, and

said anode being sospaced from said athod and grid and the said grid bein' of such coarse mesh that the impedance 0 said discharge device between said anode and said cathode is of the same order as that of said outgoing circuit.

11., Thecombination with a thermionic discharge device having a cathode, an anode and -'a control element, of an input circuit connected to said cathode and said control element, an outgoing circuit having impedance and connected to said-fanode. and

cathode, a source of electromotive force in said putgoing circuit, and means for impressmga varying electromotive force upon said input circuit, said cathode being placed in immediate proximityto said control element but out of electrical contact therewith 'and said anode being so spaced from said cathode and control element that the impedance of said discharge device between said anode and *said cathode is approximately '-.the same as that of said outgoing circuit.

12. The combination with a thermionic discharge device having a cathode, an anode,

w p and a control element, of an input circuit 8; The combination with a 'thermlomc connected to said cathode and said control element, an outgoing circuit having impedpressing a varying electromotive force upon said input circuit, said cathode, anode and control element being so placed that the im pedance'of that portion of the input circuit which is within the discharge device is made as small as possible without introducingdis ioo turbing mechanical or electrical variations" under working conditions, and the impedance of that part of the outgoing circuit which is within the discharge device is made of the same order as that of the effective impedance of that part of the outgoing circuit which is external to the discharge de-,

13. The combination with a thermionic discharge device having an anode, a cathode, and an impedance varying element, of an input circuit connected to'said impedance varying element, a-source of variable electromotive force in said input circuit, a a

source of electromotive force connected to said anode and cathode, anda work circuit connected to said anode and cathode, the impedance of said discharge device between said cathode and anode being of the same or.-

.der' as that-of said work circuit.

14. .The combination with a thermionic discharge device having an anode, a cathode, and an impedance varying element, of an input circuit connected to said impedance varying element, a source of variable electromotive force in said input circuit, a

source of electromotive force connected to said anode andfcathode, and a work clrcuit non-magnetically connected to said anode and cathode, the impedance of said discharge tdevice between said cathode and said cathode and anode being of the same order as that of said work circuit, the variable power delivered to said work circuit being much greater than that. supplied by said input circuit, while the variable voltage delivered is correspondingly less than in said inputcircuit.

16. Means for amplifying energy without substantial voltage amplification, comprising a vacuum discharge tube having aninput and an output circuit, a source of variable energy to be amplified connected in said input circuit, and a translating device to which the amplified energy is delivered connected in said output circuit.

17 Means for amplifying energy without substantial voltage amplification comprising an electric discharge device having an-anode, .a'cathode and a current control element, an

' input circuit and an output circuit for said device, a source of variable energy to be amplified connected in said input circuit. and a translating device to which the amplified en ergy is delivered connected in said output circuit.

18. Means for amplifying energy without impedance of that portion of said output circuit which is within said discharge device being of the same order of magnitude as the impedance of said translating device.

19. The combination with an electronic discharge devicehaving an anode, a cathode and an impedance varying element, of an circuit and an output circuit therefor,

means for producing a variable electromotive force in said input circuit, a source of electromotive force in said output circuit, and translating means for utilizing the va- ,riable current of said output circuit, said impedance varying element being in the form of a dlscontinuous conductlve surface,

' the ratio of conductive surface to open space being so low that, for the impedances and voltages employed outside said device, the device operates to amplify the variable energy in said input circuit without amplifying the voltage. 20. The combination with an electronic discharge device having a cathode, an anode and a grid, of an input circuit and an outa variable electromotive force in said input circuit, a source of electromotive force in said output circuit, and translating means for utilizing the variable current of said output circuit, said anode bein so close to said cathode and said grid being of such coarse mesh that, for the impedances and voltages employed outside said device, the device operates to amplify the variable energy in said input circuit wit out amplifying the voltage.

21. The combination with a thermionic discharge device having a cathode, an anode and a grid, of an input circuit and an output circuittherefor, means for producing a a put circuit therefor, means for producing variable electromotive force in saldinput Oil-r cuit, a source of electromotive force in saidoutput circuit, and translating means, for utilizing the variable current of said'output circuit, said cathode being located in immediate proximity to said grid but out of contact therewith, and the grid being of such coarse mesh, that for the impedances and voltagesemployed outside said device, the device operates to amplify the variable energy in said input circuit without amplifying the voltag 22. The combination with an electronic discharge devic having a cathode, an anode and a grid, of an input circuit and an output circuit therefor, means for producing a variable electromotive force in said input circuit, a source of electromotive force in said output circuit, and translating means for utilizing the variable currentof said output circuit, said cathode being placed in emmediate proximity to said grid, butout of contact therewith, said anode being so close to saidcathode, that for the impedances and voltages employed outside said device, the device operates to amplify the variable energy in said input circuit without amplifying the voltage.

23. The combinatioin with an electronic discharge device having a cathode, an anode and an impedance varying element, of an input circuit and an output circuit therefor, means for producing a variable electromotive forcein said input circuit, a source of electromotive'force in said output circuit and translating'means for utilizing the variable current of said output circuit, said cathode, anode and impedance varying element being so spaced that for the impedances and voltages employed outside said 24. Means for amplifyingenergy without substantial voltage amplification comprising an electric discharge device havin an anode, a cathode and a current control e ement, an

input circuit for said device, a source of variable energy to be amplified connected in said input circuit, and a work circuit to "which the amplified energy is delivered nonmagnetically connected in said output circuit.

25. A thermionic repeater having its cathode and its-output electrode spaced apart a distance suitable for producing a desired. "ratio of output voltageto input voltage and having its input electrode in immediate proximity to said cathode but out of electrical contact therewith and closer to said 15 having its input electrode as close as po sible to said cathode without contacting therewith and closer to said cathode than to saidoutput electrode. v r

In witness whereof, I hereunto subscribe 2a 7 my name this 29th day of July A. D., 1918.

HAROLD DE F. ARNOLD. 

